1. Field of the Invention
This invention relates to a linear motion guide unit suitable for use in environments where foreign substances are likely to be encountered, such as in a machine tool.
2. Description of the Related Art
Conventionally, linear motion guide units are used, for example, for proper positioning of a workpiece on a machine tool, and these days a linear motion guide unit without a cover or the like is increasingly often used with unprotected guide rails with a view to a reduction in size and in cost of the apparatus. When such a linear motion guide unit with unprotected guide rails is used in an environment where foreign substances such as chippings are generated, the foreign substances adhere to the surfaces of the guide rails. If the adhering foreign substances enter the slider or the sliding face of the guide rail, they may interrupt the smooth movement of the slider, causing a failure.
To avoid this, a seal member is provided on the outer side of the slide to prevent foreign substances from entering the sliding area. A linear motion guide unit is additionally provided with a scraper outside the seal member, or it alternatively supplies oil to a guiding face for suspending the foreign substances, in order to keep them out.
Among the linear motion guide units of such a type, Japanese Patent Application No. 2007-319697 filed by the present applicant discloses in particular one designed to be capable of sufficiently supplying oil to the guiding face, with improved durability of the sealing member.
As shown in FIGS. 7 and 8, the conventional linear motion guide unit comprises a guide rail 1 and a slider 2 slidably straddled on the guide rail 1, and also rubber end seals 4 which are respectively mounted on the outer sides of the end caps 2a respectively attached to the opposing ends of the slider 2. In addition, resin-made wiper seal assemblies 6 are respectively mounted on the outer sides of the end seals 4 with the interposition of resin-made mounting plates 5.
As shown in FIG. 9, each of the end seals 4 is formed of rubber baked on a cored bar 4a, and includes a lip 4b having an end pressed against the guide rail 1 so as to seal the gap between the slider 2 and the guide rail 1.
The mounting plate 5 attached to the outer side of the end seal 4 is shaped to create a space 10 on the side facing the end seal 4 for protecting the lip 4b as shown in FIG. 9.
The wiper seal assembly 6 attached to the outer side of the mounting plate 5 has a recessed portion with a bottom face 6a facing toward the end seal 4 as shown in FIGS. 9 and 10. In the recessed portion, two oil-impregnated wiper seals 7 and a metal-made sealing plate 8 are mounted. The sealing plate 8 is provided for giving firmness to the wiper seals 7, which are oil-impregnated materials, to prevent them from being easily deformed. In turn, a scraper 9 is provided on the outer side of the wiper seal assembly 6.
As illustrated in FIG. 11, the mounting plate 5, the end seal 4 and the end cap 2a are secured to the casing 2b of the slider 2 with bolts 11. Then, the scraper 9 and the wiper seal assembly 6 are secured to the mounting plate 5 from outside the scraper 9 with other bolts 12 and nuts 13 provided on the mounting plate 5. The reason for such use of two sets of bolts 11, 12 is that, when all the components are mounted on the outside of the end cap 2a, the length in the sliding direction of the slider 2 is increased, causing the difficulty in using one set of long bolts to mount all the components.
Note that reference numeral 3 in FIG. 11 denotes an oil-impregnated member fitted into a recessed portion formed in an end face of the end cap 2a. The oil-impregnated member 3 is placed more inward than the end seal 4 for supplying oil to rolling elements and/or the like which are set in the end cap 2a. 
In a linear motion guide unit as described above, when the slider 2 reciprocates, large foreign substances on the guide rail 1 are removed by the scraper 9, and the foreign substances slipping through the scraper 9 are prevented from entering the slider 2 by the wiper seals 7 and the end seal 4. In particular, the oil supplied from the wiper seals 7 and the sliding movement of the wiper seals 7 makes it possible for the foreign substances to enter the internal area with respect to the end seal 4. As a result, the end seal 4 can maintain its high sealing performance over a long term without being damaged by foreign substances.
As described above, a conventional linear motion guide unit has an arrangement in which an end seal 4, a mounting plate 5, a wiper seal assembly 6 containing wiper seals 7 and a sealing plate 8, and a scraper 9 are disposed in this order on the outer side of each of the end caps 2a of the slider 2. In this manner, the conventional linear motion guide unit having high sealing performance includes a large number of components mounted on the opposing ends of the slider 2. For this reason, much time and effort are required for mounting each component. In addition, the size of the slider 2 in the sliding direction is increased, thus disadvantageously causing the impossibility of a reduction in size of the linear motion guide unit.